Parent U.S. Pat. No. 6,267,044 describes a toaster which contains heating elements optimally designed and positioned for toasting and provides the means to preheat the toasting elements to optimal thermal conditions for toasting before introducing the bread or other material to be toasted into the toasting environment. The novel toaster design disclosed in that patent includes also added means to create the optimal conditions for baking, warming, defrosting or a combination thereof. The design geometry, size and thermal environment of the relatively ubiquitous conventional toasters have not proven satisfactory for quality baking, defrosting or warming. By contrast this toaster will perform these functions faster and better than conventional baking ovens common to virtually all kitchens.
Conventional baking ovens that have been used for centuries are designed with horizontal shelves to cook food in horizontal containers that are slowly raised to elevated temperatures by heated air. Food in those containers is heated primarily by contact with the hot horizontal container or by contact with adjacent food in turn heated by contact with the container.
In more recent times motor driven fans have been introduced in ovens to circulate the air around the containers and over the top of foods in horizontal containers or horizontal shelves. Large electrical heaters have been added on the ceiling, floors and side walls of ovens to heat the air more rapidly. Horizontal shelves are provided universally as the means to hold food containers and in some cases to position bread or other foods horizontally in close proximity to a horizontal mounted heater that will toast or broil one side at a time. The efficiency of the toasting operations is very poor taking many minutes to toastxe2x80x94leaving a dry relatively unappetizing product. Large ovens of that sort take 10 or more minutes just to reach baking temperatures and substantial time to complete the baking because of inefficient heat transfer to the food. No provision is made in such ovens to insure intimate and direct contact with all surfaces of the food when that food is particulate or simultaneously with both sides of the food if the food is planer such as steaks, patties, and waffles. An exception to that is the rotisserie that secures larger foods on skewers and rotates them before the heated air, flames, or heated elements.
The present invention is directed to techniques for optimal baking cycles in the unique toaster of parent U.S. Pat. No. 6,267,044.
This invention describes the means and mechanism to hold particulate food within a toaster so that there is direct and intimate contact between heated air and virtually all the foods surface area to insure rapid and uniform heating of the food by naturally convective transfer from hot air at baking temperatures in combination with programmed temperature radiant energy from toasting elements and at least one auxiliary heater operating at optimum temperatures which are different from those that must be employed in an optimal toasting cycle. This programmed combination of heating by the hot air and radiation provides optimum baking rates without overheating the exposed surfaces of the food in such a manner as to create excessive or burning of the food surface. By this new methodology and by the close proximity of the heating system and the toasting elements it is possible to optimize the baking conditions for the effective baking of hundreds of uncooked or xe2x80x9cprecooked but not brownedxe2x80x9d foods available for quick bake-and-serve dishes. Unlike conventional ovens and toasters which cook slowly and unevenly, the means disclosed here bakes rapidly and uniformly simultaneously on virtually all surfaces of particulate foods creating tasty uniform temperature foods as a result.
Many ovens and so called toaster-ovens can be used for toasting but the toasted food lies flat and must be turned over to complete the toasting or to achieve relatively uniform toasting on each side. Those heater elements are not optimized for toasting. In the baking mode in conventional ovens there is little motion of the air over or through the food, rather the air is relatively quiescent. Convection ovens with fans generate a general air flow within the oven but these are not designed to circulate air through a bed of particulate foodxe2x80x94such as frozen french fries. Conventional toasters are used today in an attempt to xe2x80x9ccookxe2x80x9d many of the frozen xe2x80x9cprecooked but not brownedxe2x80x9d foods by simply repeating the toasting cycle several times. The results are very disappointing creating overcooked and undercooked areasxe2x80x94sometimes burnt before getting sufficiently warm on the interior. Good baking requires less intense heat in order that the interior can be warmed sufficiently before the surface is overheated or burnt.
No provision is made in such ovens for vertical open baskets to hold the food and to allow air to pass through a bed of particulate foodxe2x80x94such as frozen french fries.
There have been attempts to offer toasters that combine the toasting and baking functions such as U.S. Pat. No. 2,862,441 by W. A. Schmall (Dec. 2, 1958) assigned to General Electric. This describes a combination unit which uses movable mirrors to redirect radiant energy upward for toasting or downward to a separate baking compartment. That baking function can not be particularly effective since the heat was applied only by the mirrors to one side of the food.
In contrast to prior art the subject baking appliance is designed first as an optimal toaster Baking is accomplished in the same space with the use of an auxiliary air heater mounted below the baking space and with the use of sophisticated electrical and electronic control of the toasting elements to equalize air temperatures and to generate natural convection currents of the heated air through and around vertically configured open mesh basket that contains the particulate food. The relative amounts of heat provided by the toasting elements and by the auxiliary air heater are electronically controlled to optimize the baking rate while avoiding excessively localized heating of the food surface by either the localized air temperature or the radiation from toasting elements. The toasting elements are segmented so that they can be heated individually or together and thus temperature is controlled so as to optimize the air temperature along the vertical face of the vertical open mesh basket which holds the food to be baked.
U.S. Pat. No. 6,267,044, the details of which are incorporated herein by reference thereto, describes many of the novel aspects of this new batch toaster in particular means for retaining the food to be toasted remote from the toasting zone until the thermal conditions in the toasting zone are optimal for toasting. By that means the bread or other food to be toasted is when entered into the toasting zone, toasted rapidly avoiding unnecessary drying of the food that would otherwise take place before the ambient thermal conditions are optimal for toasting of the food surface. Consequently the toasted foods loses less internal water and can be crisp on its exterior surface while retaining more of its internal moisture. The food to be toasted is placed on a carrier of some sort and transported either manually or automatically into the toasting zone when that zone is thermally optimal for toasting.
For toasting to occur rapidly, and thus reduce the loss of moisture from the food, it is best that heat transfer be largely by radiation and less by a combination of hot air conduction and convection where heat transfer is inherently slower limited by the thin layer of air in the boundary layer adjacent the food surface. Heat transfer through such boundary layers is inherently slower while radiation can pass literally at the speed of light uninhibited from the radiant source onto the food surface. When toasting this speed is advantageous. When baking one has to monitor and control carefully the amount of radiant energy so as to avoid burning the surface of the food before the interior is adequately baked. For the interior of the food to be baked sufficiently, heat must be first transferred to the surface of the food, whence heat must travel by conduction to the middle of the food thickness. The latter takes time because the thermal conductivity of food is poor and the amount of heat transferred is driven only by the elevated surface temperature of the food. The higher the surface temperature the better up to the point where the surface is overheated and begins to burn or overcook. Consequently the surface temperature must be carefully controlled and limited to avoid burning but it must be hot enough to drive effectively the heat below the food surface where it is needed to evaporate excess water and to dehydrate and crosslink the food proteins or break chemical bonds.
Toasting a surface phenomenon, can be forced to occur rapidly. By contrast baking rates are limited by the slow transfer of heat through the full thickness of foods. Baking cannot be rushed without danger of burning the surface. This is why toasters are notoriously poor for baking. The intensity of toasting elements must be moderated if they are used during extended baking to assist in heating the surface of foods. Radiation from toasting elements will not shine onto all food surfaces within a bed of particulate food. Shadowing effects limit the effectiveness of direct radiation. Heat for the surface of interior particulate surfaces can be well provided by convective and conductive transfer from hot air circulating around and between the particulate food.
From the above it is clear that a thermal environment ideal for toasting is not suitable for quality baking. Similarly the environment optimal for baking is totally unsatisfactory for toasting. What this inventor has discovered is that it is possible to bake efficiently and rapidly in the toasting space by using segmented electrical toasting elements operating at reduced temperature as auxiliary heaters to supplement a remote efficient heating means to elevate the air temperature within the enclosure and to generate natural convection current around and through a bed of particulate food adjacent to the toasting elements. The baking process can be optimized by programming independently the temperature of the segmented toasting elements and the remote heating means throughout the baking cycle. In the relatively short initial heat-up phase of the baking cycle (approximately 1xc2xd minutes) both the upper and lower toasting segments are powered to an elevated temperature equal to or slightly lower than their temperature when toasting. This provides an initial burst of radiant and convective heat transfer that elevates the temperature of the food surface and hastens the overall temperature rise of the enclosed air, the oven walls and the baking basket. In the initial phase the remote heater also operates at or close to full power to hasten the heat-up process. Temperature within the baking space is monitored to determine when it has reached the desired baking temperature. After that time usually less than 2 minutes, the toaster elements are operated at reduced temperature and the power applied to the remote heater and to the toaster element is controlled to maintain the oven temperature at the desired temperature.
Any of a variety of electrical control means can be used to program during each portion of the baking cycle the appropriate amount of power to the toasting elements and to the remote heating means. A solid state relay controlled by an oven temperature sensing means proved particularly effective for controlling power to the various heating elements.
This inventor has found that the uniformity and speed of baking of particulate foods is enhanced significantly if the food is held in an elongated vertically oriented mesh basket of cross section sufficiently small that heated air can readily pass by naturally convective means through the basket thus contacting efficiently the surfaces of the particulate food held therein. Using a specific arrangement of heating elements and by employing a vertical basket of approximately 1xc2xe to 3 inch thickness (between the large vertical mesh faces) natural convection of the heated air passes rapidly through such a basket insuring that the particulate food is uniformly heated and baked throughout the basket.
A vertical configuration of the baking basket is optimal and it is consistent with the toasting geometry optimal for toasting as described herein and in parent U.S. Pat. No. 6,267,044. The elongated vertical orientation of the baking basket allows toasting heating elements of similar orientation to be used effectively to aid in the heating process and to apply heat uniformly to the face of the elongated vertical baking basket.
By using an elongated relatively high power heater (approximately 600-1000 watts) under the basket, air heated by this means rises naturally by virtue of its reduced density along the vertical faces of the mesh basket. By physically offsetting the heater slightly, on the order of a quarter inch or so from the long center line of the baking basket it was found that there is greater air flow up one side of the basket creating enough pressure difference between the faces of the basket to force a significant fraction of the hot air through the thickness of the mesh and across the surfaces of the cooler particulate food. It was found convenient to use a high temperature elongated source such as a cal-rod or a quartz-enclosed conventional hot wire heater. Because of the high temperature required for efficient heat transfer to air by such a source it may be hot enough to radiate significant energy. In that event the bottom of the mesh basket is best shielded from the direct radiation emitted by the heating source. One way to prevent the direct radiation from shining on the food basket is to locate that source in a relatively open but roofed compartment below the food basket. The mesh baking basket can be supported by, but spaced above an integral solid metal base. The bottom of the open mesh basket should optimally be positioned at least xe2x85x9cxe2x80x3 above any such base. By these means hot air can ascend up through the mesh bottom of the basket. Either the metal base or the roof of the heater compartment will shield the food from direct radiation from the lower heater.
More than one air heater can be used below the baking basket and their positioning can be arranged to provide greater air flow up one face of the basket and then pass the other to create a pressure difference across the faces of the basket and flow through the basket.
The elongated vertical configuration for the baking basket has proven ideal because it conforms directly with the planar geometry of the toasting heater boxes and it allows air heated from below to pass uniformly upward along and across the entire large faces of the baking basket and through the particulate food. The advantages of this arrangement can be readily visualized in comparison to the use of conventional horizontal pans, horizontal trays or open mesh shelving. None of these conventional baking configurations offer the possibility simultaneously for the symmetry and proximity of auxiliary planar heaters such as the toaster elements adjacent both major faces of the basket as described here nor do they offer opportunity for simultaneously creating uniform naturally convective air currents along both sides of the food basket and through its food bed.
The effectiveness of the natural convective hot air currents through the cool food was demonstrated by detailed temperature measurements of the food temperature and the air temperature adjacent to the baking basket. It was observed when the long axis of the lower heater was offset xc2xc inch or so from the lower center line of the basket, convective air currents through the food increased sufficiently to equalize the air temperature adjacent to the food to that of the rising main air stream. When the lower heater was centered the air temperature adjacent the cool food dropped below the temperature of the air above and below the food level reflecting much less convective circulation through the food. When the heater was set off center the food cooked (reached ultimate temperature faster) and it was cooked more uniformly throughout the food bed.
This unique toaster and baker is designed to optimize separately its performance for each of these two functions. None of the known batch toasters preheat the toasting element and toasting environments before toasting to create the crispy yet moist texture. None of the known batch toasters are effective for baking. Toaster ovens are available that offer the ability to either toast or bake. They do not offer means to optimize the toasting environment before introducing the bread. Neither do they offer optimal means to bake in a vertical basket by combining the heating advantages offered by precise and programmed control of adjacent planer toasting elements and a remote heater to generate efficient heated air convection currents past and through a bed of particulate food.